Method - Turtle Tipping

Method - Turtle Tipping

First, get a Gold Flower in your inventory (either from a Star House or the World 2 Rainbow Course), then, go to one of the good turtle-hopping levels (like Mushroom-1, see also Infinite 1-Ups), and proceed to turtle hop. Instead of getting 1-Ups, you'll get 50 coins each jump. Unfortunately, after getting about 1,000 coins, the shell will break!

However, there is a workaround to this.

In Mushroom-1, if you go to the area with the turtle hopping trick and count 20 or so hops then leave and go out of the pipe, you can continue to return and earn coins indefinitely (until the timer runs out.)

in Star-1, there are four turtles that can be used, which means you can repeat the course multiple times earning at least 4000 coins every time.

This video from Teto3X shows how to get infinite lives; these can be adapted with a gold flower for coins.